Process for regenerating used catalysts by means of hydrogen peroxide aqueous solution stabilized with an organic compound

ABSTRACT

The process has as an object the regeneration of catalysts containing at least one contaminating metal of the vanadium, nickel and iron group. The operation is conducted as follows: 
     (a) The catalyst (1) is roasted in the presence of an oxygen-containing gas so as to remove at least 90% of the sulfur; 
     (b) The catalyst obtained in step (a) is contacted with a hydrogen peroxide aqueous solution containing at least one organic compound comprising an acidic functional group, so as to remove at least 10% of the deposited metals of the vanadium, nickel and iron group; and 
     (c) The regenerated catalyst (11) is separated from the aqueous solution of metal ions (5). The latter can be regenerated by passage over a complexing resin (6). 
     The process is applicable to the regeneration of used catalysts, particularly to hydrotreatment catalysts in the oil industry.

This is a continuation-in-part of application Ser. No. 836,866 filedMar. 7, 1986 now U.S. Pat. No. 4,714,688 issued Dec. 22, 1987.

BACKGROUND OF THE INVENTION

This invention concerns a process for regenerating a catalyst at leastpartially deactivated after use in the treatment of a hydrocarbon chargecontaining at least one heteroelement from the sulfur, oxygen andnitrogen group and at least one metal from the vanadium, nickel and irongroup, said deactivation resulting from the deposition of said metal onthe catalyst initially formed of an inorganic carrier and at least oneactive metal or compound of active metal, selected from the groupconsisting of nickel, cobalt and molybdenum. Most often, thecombinations nickel-molybdenum and cobalt molybdenum are particularlyconcerned.

This invention relates more particularly to the regeneration ofcatalysts used in the hydrotreatment and/or hydroconversion of crudeoils and oil cuts of high boiling point, for example above 350° C., suchas straight-run or vacuum residues, shale oils, bituminous sand, asasphalt fraction or a fraction of liquid hydrocarbons obtained by coalliquefaction, straight-run or vacuum gas-oils or even fuel oils.

It may also be used as a basic process for the recovery of substantialmetal amounts from catalysts used for treating heavy oil charges. Forexample, by treating 16,000 m³ /day of Orinoco oil, 7,000 tons ofvanadium can be recovered.

During the operations of hydrotreatment (hydrodesulfurization,hydrodenitrogenation, hydrodemetallation), of hydrocracking or ofcatalytic cracking, the catalyst is progressively covered with depositsof coke and metals originating from the treated heavy charges.

Vanadium, nickel and iron are the three most important metals concernedbut the invention is not limited to these three metals only.

The retention of metals and coke on the catalyst carrier results in adecrease of the pore volume and of the specific surface, therebylimiting the access of hydrocarbon molecules to the catalyst sitesinside the catalyst particles. The catalyst activity thus decreasesprogressively or may be nullified when all the pores of the carrier arefilled with vanadium, nickel and/or iron.

Many papers and patent applications have as their object theregeneration of catalysts poisoned by the above-mentioned metals.

In the known processes, hydrogen peroxide has often been used, eitheralone or as an aqueous solution, or combined with reducing washings orwashings with diluted solutions of inorganic acids (nitric, sulfuric,hydrochloric acids), or associated with heteropolyacids or with basicsalts as, for example, sodium carbonate.

On the other hand, vanadium and nickel extractions by aqueous solutionsof hydrogen peroxide have been generally performed from these metals inthe state of sulfides or directly on used and/or exhausted catalysts, orafter a presulfurization with various sulfurizing agents, mostly withhydrogen sulfide, when the used catalysts do not contain a sufficientamount of sulfur.

According to the usual explanation, this presulfurization causes themetals to migrate to the surface of the catalyst particle. Vanadium andnickel extraction is accordingly easier.

U.S. Pat. No. 3,562,150 discloses vanadium extraction fromthermodynamically stable vanadium sulfides (V₂ S₃, V₂ S₅). This patentestablishes the fact that, in order to obtain the best results, vanadiumextraction from the used catalysts by hydrogen peroxide solutions mustbe performed before the roasting step in the presence of air at 510° C.,for 16 hours. When reversing the order of these two treatments, themetal extraction and the activity of the regenerated catalyst are not asgood.

The commercial processes for demetallation of used catalysts, e.g., theSINCLAIR DEMET PROCESS, published in "The Oil and Gas Journal" of Aug.27, 1962, pages 92-96 and in the article entitled "The demetallizationof cracking catalysts" published in I & EC Product Research andDevelopment, Volume 2, pages 238-332, December 1963, or in "HydrocarbonProcessing & Petroleum Refiner", volume 41, no. 7, July 1962, indicatesthat metals extraction by hydrogen peroxide aqueous solutions must bepreceded by a presulfurization step with hydrogen sulfide.

U.S. Pat. No. 4,101,444 indicates that metal extraction by means ofhydrogen peroxide must be preceded by a washing treatment with areducing agent consisting of sulfur dioxide dissolved in water.

Finally, U.S. Pat. No. 4,268,415 states that metal extraction isdirectly performed from metal sulfides of used catalysts after washingwith organic solvents and/or must be preceded by a previoussulfurization with hydrogen sulfide when the catalyst to be treated hasan insufficient sulfur content. This patent shows that the addition of asuitable amount of hydrogen peroxide clearly improves the metalextraction by heteropolyacids.

The applicant's work has shown that the known processes suffer from manydisadvantages:

substantial etching of the catalyst carrier, when the latter containsalumina or silica-alumina or a zeolite, by the sulfuric acid formedduring the extraction of the metals in the sulfide state or by steam andnitric acid extraction U.S. Pat. No. 4,501,820

substantial decomposition of hydrogen peroxide to water and oxygen gas,in contact with inorganic catalyst carriers and by the extracted metalions, making the process rather uneconomical,

reactivation only to an insufficient extent, resulting apparently froman insufficient removal of the undesirable metals.

SUMMARY OF THE INVENTION

The invention has as an object a process for regenerating catalysts withreduced consumption of hydrogen peroxide, while obtaining a high rate ofmetal extraction and a high rate of reactivation.

In order to reduce to a minimum or even to avoid the decomposition ofhydrogen peroxide to water and oxygen gas, by contact with the catalystcarrier and with the extracted metal ions and to avoid any substantialetching of the carrier, hence obtaining an economical process forextracting the contaminating metals from the catalysts, the presentinvention provides a process for regenerating an at least partiallydeactivated sulfur-containing catalyst after its use for thehydrotreatment of a hydrocarbon charge containing at least one sulfur,oxygen and nitrogen heteroelement and at least one vanadium, nickel oriron metal, said deactivation resulting from the deposit of at least oneof said metals onto the catalyst. The catalyst initially comprises aninorganic carrier and at least one active metal or compound of an activemetal selected from the group of nickel, cobalt and molybdenum; saidprocess consists essentially of the following successive steps:

(a) The catalyst is roasted in the presence of an oxygen-containing gasso as to remove at least 90% of the sulfur,

(b) the catalyst obtained in step (a) is contacted with a hydrogenperoxide aqueous solution containing at least one organic compoundcomprising at least one acidic functional group so as to remove at least10% of the deposited vanadium, nickel or iron metals, and

(c) the regenerated catalyst is separated from the aqueous solution ofmetal ions.

The roasting operating conditions are so adjusted as to remove at least90% of the sulfur, preferably at least 99%, and to reduce to a minimumthe formation of metal sulfates. The metal sulfides are converted to thecorresponding oxides, for example the vanadium metal sulfides are mainlyconverted to vanadic anhydride (V₂ O₅).

Simultaneously, the coke or carbon deposited on the used catalyst, iseliminated. Depending on the charge and the operating conditions of thehydrotreatment the cake or carbon deposited may be about 0.1 to 20% byweight of carbon and most often about 1.0 to 10% by weight,

The sulfur also deposited onto the catalyst may be equal to about 1 to30% and preferably is 5 to 20% by weight.

Generally, the roasting temperatures range from 300° to 600° C.,preferably from 450° to 550° C. Higher roasting temperatures are liableto modify the carrier structure, mainly in presence of water. So, theroasting step is performed without steam at the temperature range asabove. Otherwise, the mechanical strength is considerably lowered.

The ratio of moles of oxygen gas/gram-atoms of sulfur of the metalsulfides, necessary to convert the metal sulfides to the correspondingoxides, is advantageously higher than 2, preferably equal to or higherthan 10.

On the other hand, the air flow rate must be sufficient to quicklydischarge the formed sulfurous and/or sulfuric anhydride to the outsideof the roasting zone, thus avoiding the sulfurization of the oxides,which, as sulfates, are difficult to extract. The oxygen content and theair hourly flow rate must be sufficient to maintain at all times asulfurous anhydride content lower than 10 ppm.

The roasting time is generally from 2 to 15 hours, preferably from 2 to7 hours for catalysts of low sulfur content and 8 to 15 hours forcatalysts of high sulfur content (higher than a few percent by weight,e.g. substantially higher than 3%).

In the presence of an aqueous solution of hydrogen peroxide and of astabilizing organic compound, the metals, mainly present as oxides, areextracted as peroxidized ions, vanadium, for example, to a major extentas pervanadic ions [VO(O₂)]⁺ and/or VO₂ ⁺.

The stabilizing organic compound may be added to the hydrogen peroxideeither before the step of contacting the catalyst with the solution orduring said step.

The organic compounds comprising at least one acidic functional groupmay consist of carboxylic acid, acids alcohols and their mixtures.Hydrocarbon polycarboxylic acids and hydrocarbon mono-and polycarboxylicacids comprising at least one alcohol group are preferred.

Very efficient organic compounds for stabilizing hydrogen peroxideaqueous solutions in contact with catalytic carriers, providing for highextraction rates of the metals with a minimum consumption of hydrogenperoxide, are preferably selected from the group formed of salicylicacid, L(+) ascorbic acid, citric acid, maleic acid, oxalic acid andglycolic acid.

The stabilizing organic compound is used in an amount ranging forexample from 0.1 gram per liter up to saturation, preferably from 2 to10 grams per liter and more preferably from 3 to 7 grams per liter.

The aqueous solutions may contain from 0.5 to 70% by weight of hydrogenperoxide, preferably from 1 to 30% by weight and, more preferably, from5 to 20% by weight.

The stabilized hydrogen peroxide aqueous solution according to theinvention may be pumped over a catalyst fixed bed operated for examplewith hourly flow from 0.5 1/h to 30 1/h, preferably from 5 1/h to 20 1/hper kg of catalyst metal oxides formed after roasting, and for a timeof, for example, 1 to 6 hours.

The catalyst may comprise at least one active metal or compound ofactive metal selected from the group of Ni, Co and Mo; Generally, it maycomprise about 6 to 30% by weight of MoO₃, about 1 to 6% of NiO and/orabout 1 to 6% of CoO. Its inorganic carrier such as conglomerates (forexample balls, extrudates) has a particle diameter of at least 0.5 mmand may be alumina, silica, silica-alumina or a zeolite carrier, forexample of faujasite structure.

The operation is preferably conducted in the absence of visible lightand at a temperature from 0° to 80° C., preferably from 10° to 40° C.,so as to avoid any substantial decomposition of hydrogen peroxide.

It may be particularly advantageous to subject the solution of metalions obtained in step (b) to a step of contracting with a complexingresin having a complexing power for the metals of the solution, therecovered hydrogen peroxide solution being thus free of at least themajor part of the metals. This solution may be reintroduced, at leastpartly with the hydrogen peroxide solutions, in step (b).

The metals are retained on the complexing resin as chemical complexes,generally inactive with respect to hydrogen peroxide. The complexingresin is then regenerated to recover the metals.

Various complexing resins of the trade can be used such, for example, asthose sold under the trade marks DUOLITE, AMBERLITE or DOWEX whosepolymer skeleton may be, for example, polyacrylic or polystyrenic andwhose functional groups having complexing power with respect to theextracted metal ions are, for example, amidoxime, iminodiacetic, and/oraminophosphonic groups.

When using, for example, DUOLITE ES 346, the solution recovered at theoutput of the resin column contains at most 2 ppm of vanadium after atime to passage of 6 hours. With amidoxime as functional group ofcomplexing power, the metal ions are retained on DUOLITE ES 346 asamidoximates.

Finally it has been observed that the metal complexes formed on theresin are inactive with respect to hydrogen peroxide since substantiallyno decomposition of hydrogen peroxide occurs.

The metal ions retained on the complexing resin may be subsequentlyremoved by known methods.

The operating conditions for passing the solution of metal ions over thecomplexing resin may be the same as those stated above for the passageover the proper demetallation column, i.e. a flow rate of the solutionfrom 0.5 to 30 liters/hour per kilogram of resin, for a time from 1 to 6hours, preferably in the absence of light, at a temperature from 0° to80° C., preferably from 10° to 40° C.

BRIEF DESCRIPTION OF THE DRAWING

The invention is further illustrated by the FIGURE of the accompanyingdrawing, showing, by way of non limitative example, a flow sheet foroperation of the process.

The catalyst is roasted in a furnace (1) of known type. It isintroduced, through line (2), into an opaque demetallation reactor (3),thermoregulated at room temperature, for example by water circulation.

A stabilized hydrogen peroxide aqueous solution according to theinvention is fed, through line (4) to reactor (3) and scavenges thefixed bed of used catalyst.

The aqueous solution of hydrogen peroxide with the so-extracted metalions is fed, through line (5), to an opaque retention column (6),thermoregulated at room temperature and filled with a complexing resin.The hydrogen peroxide solution recovered from the column bottom (6),through line (7), may optionally be recycled through line (10). Anoptional additional amount of hydrogen peroxide and of stabilizer may beadded through lines (8) and (9).

The catalyst, free of the major part of its contaminating metals, iswithdrawn from the demetallation column (3), through line (11).

The resin is then subjected to a regeneration step, to recover themetals.

It may be observed that the catalyst may be arranged as moving bed,expanded bed or fluid bed instead of fixed bed.

The demetallation rate DR, in percent by weight, is calculated from thedeterminations of the catalyst metal contents before and afterextraction of the metals, by the x-ray fluorescence method. It isexpressed as:

    DR=(Qi-Qf)/Qi×100

Wherein:

Qi is the metal amount, in gram, contained in the amount of catalyst, ingrams, subjected to treatment, and

Qf is the metal amount, in gram, contained in the amount of solid, byweight, remaining after extraction.

The hydrogen peroxide in aqueous solution is determined by the cerimetrymethod.

The hydrogen peroxide consumption, expressed in mole percent, isdetermined by difference between the respective contents of the solutionat the input of the demetallation column and at the output of thecomplexing resin column. as follows:

    % molar consuption: (Ni-Nf)/Ni×100,

wherein:

Ni is the total number of hydrogen peroxide moles contained in thevolume of solution fed to the input of the demetallation column reactor.

Nf is the total number of hydrogen peroxide moles contained in thevolume of solution recovered at the output of the complexing resincolumn.

The metal contents of the extraction solution are determined by theplasma spectroscopic method.

The sulfur content of the deasphalted BOSCAN oil charge, before andafter the catalytic tests, has been determined by the fluorescencemethod.

The hydrodesulfurization rate (HDS), expressed in %, is:

    HDS %=(So-S)/So×100,

wherein:

So is the sulfur content of the charge, in percent, before the catalytictest, and S is the sulfur content, in percent, of the charge after thecatalytic test.

The amounts of metals (nickel, vanadium and iron) of the deasphaltedBOSCAN oil charge are determined by atomic absorption and theirelimination rate is expressed as follows:

    HDM %=(Mo-M)/Mo×100

Mo and M being the respective contents of metals (nickel, vanadium andiron) in the charge before and after the catalytic test.

EXAMPLES

The following non limitative examples illustrate the invention:

EXAMPLE 1

A nickel-molybdenum catalyst, initially containing 1.75% by weight ofnickel, 7% by weight of molybdenum and 0% of vanadium on a macroporousalumina inorganic carrier having a porosity of 105 cc/100 g, a specificsurface of 110 m2/g and a density of 0.75 cc/g, is activated by roastingat 500° C. for 2 hours in the presence of an air stream flowing at arate of 60 liters/hour per 300 g of catalyst, followed with asulfurization step with a 2% by weight solution of dimethyl-disulfide ingas-oil at 350° C., at a VVH of 2, for 5 hours.

It is then used for 1,000 hours in the hydrotreatment of a deasphaltedBOSCAN oil containing 550 ppm of vanadium, 60 ppm of nickel and 5.06% byweight of sulfur.

After 1,000 hours of operation, the used catalyst contains (in % byweight):

    ______________________________________                                        Vanadium:                                                                             30.9%    Nickel: 2.89% Molybdenum:                                                                            2.60%                                 Iron:    1.2%    Sulfur: 19.5% Carbon:   4.5%                                 ______________________________________                                    

According to the invention, the used catalyst (300 grams) is firstroasted at 500° C. in an air flow of 60 liters/hour, for 15 hours. Thesulfurous anhydride content of the gas was, at any time, lower than 10ppm. Thus 99% of the sulfur has been removed from the used catalyst.

10 gram samples of the used catalyst, two of which unroasted and tworoasted as above are each introduced into an opaque demetallationreactor, filled with polyethylene balls, as packing.

Four tests of metal extraction have been performed, for comparisonpurposes wherein:

A--10 grams of used and roasted catalyst is contacted with a hydrogenperoxide aqueous solution of the trade (9% by weight) stabilized with4.5 g/l of L(+) ascorbic acid according to the invention;

B--10 grams of used and roasted catalyst is contacted with a hydrogenperoxide aqueous solution of the trade (9% by weight), in the absence ofL(+) ascorbic acid;

C--10 grams of used and unroasted catalyst is contacted with a hydrogenperoxide aqueous solution of the trade (9% by weight), stabilized with4.5 g/l of L(+) ascorbic acid;

D--10 grams of used and unroasted catalyst is contacted with a hydrogenperoxide aqueous solution of the trade (9% by weight), in the absence ofL(+) ascorbic acid.

The pumping rate of the solution on the 10 grams of catalyst fixed bedis 180 millimeters per hour, for 3 hours.

The temperature of the demetallation column is regulated at 16° C.

The solution of extracted metal ions flowing out from the demetallationcolumn passes through a second column containing 100 g of DUOLITE ES 346as a complexing resin, also thermoregulated at 16° C.

The following table gives the tests results:

                                      TABLE I                                     __________________________________________________________________________                           vanadium content of                                                           the solution recovered                                 demetallation rate                                                                            consumption                                                                          at the output of the                                   (% by weight)   H.sub.2 O.sub.2                                                                      DUOLITE ES 346 column                                  Test                                                                              V  Ni Fe Mo (mole %)                                                                             (ppm)                                                  __________________________________________________________________________    A   85.3                                                                             80.2                                                                             75.0                                                                             71.0                                                                             33.05  <2                                                     B   70.8                                                                             53.0                                                                             65.3                                                                             65.0                                                                             74.26  <2                                                     C   80.7                                                                             76.2                                                                             70.0                                                                             60.8                                                                             82.13  <2                                                     D   64.8                                                                             46.7                                                                             57.2                                                                             60.2                                                                             100.00 <2                                                     __________________________________________________________________________

This table shows that the demetallation rate, measured on the catalysttreated according to the invention (test A) is the highest and that thecorresponding hydrogen peroxide consumption is the lowest.

It may also be observed that the retention of the extracted metal ionson the DUOLITE ES 346 complexing resin is substantially complete.

EXAMPLE 2

The purpose is to reuse the hydrogen peroxide solution recovered at theouput of the column containing the DUOLITE ES 346 complexing resin.

Test A of example 1 according to the invention is repeated twice.

Each of the two recovered solutions contains 6.05% by weight of hydrogenperoxide. Their hydrogen peroxide content is adjusted to 9% by weight,by addition of perhydrol.

Two metal extraction tests, identical to test A of example 1have beenrepeated in the following conditions:

Test I: without addition of L(+) ascorbic acid,

Test II: with addition of 0.243 g of L(+) ascorbic acid to the recovered540 milliliters (i.e. 10% with respect to the initially used content at4.5 grams/liter).

The test results are reported in Table II

                  TABLE II                                                        ______________________________________                                                demetallation rate (% by weight)                                      Test     V       Ni          Fe    Mo                                         ______________________________________                                        I        83.8    78.2        75.0  69.0                                       II       85.0    81.2        75.3  72.1                                       ______________________________________                                    

The results of test II, as compared with those of test A of example 1,show that substantially equal demetallation rates can be obtained.

EXAMPLE 3

The metals extraction treatment according to mode A of example 1 isrepeated with varying pumping rates of the stabilized hydrogen peroxidesolution according to the invention.

The demetallation rates, as determined on the treated catalysts, arereported in table III.

                  TABLE III                                                       ______________________________________                                        hourly pumping                                                                rate of the H.sub.2 O.sub.2                                                   stabilized solution                                                                       Demetallation rate (% by weight)                                  (ml/hour)   V       Ni         Fe    Mo                                       ______________________________________                                         60         52.0    47.8       49.1  39.0                                     120         66.0    62.0       64.2  53.0                                     180         85.3    80.2       75.0  71.0                                     240         85.1    80.0       74.8  71.8                                     300         86.3    79.5       75.5  70.3                                     ______________________________________                                    

The metal extraction rate is practically at a maximum for a pumping rateof 18 liters/hour per kilogram of catalyst subjected to treatment.

EXAMPLE 4

The metal extraction treatment is repeated according to mode A ofexample 1 and the demetallation rates of the treated catalysts aredetermined versus the reaction time.

The results are reported in table IV.

                  TABLE IV                                                        ______________________________________                                        Metals extraction                                                                          demetallation rate (% by weight)                                 time (hours) V       Ni        Fe    Mo                                       ______________________________________                                        1            44.1    39.6      40.8  44.0                                     2            72.2    63.6      68.0  68.0                                     3            85.3    80.2      75.0  71.0                                     4            88.9    82.0      80.0  77.2                                     5            93.0    83.7      82.7  78.4                                     6            93.7    83.9      83.5  79.8                                     ______________________________________                                    

An extraction time of, for example, 5 hours gives particularlyadvantageous results.

EXAMPLE 5

The metal extraction treatment according to mode A of example 1 isrepeated but the tests are conducted at different temperatures. Theresults are given in table V.

                  TABLE V                                                         ______________________________________                                        extraction                   H.sub.2 O.sub.2 consump-                         temperature                                                                            demetallation rate (% by weight)                                                                  tion                                             (0° C.)                                                                         V       Ni      Fe    Mo    (mole %)                                 ______________________________________                                        16       85.3    80.2    75.0  71.0  33.05                                    25       96.7    93.7    90.0  91.8  54.30                                    40       97.7    95.9    92.1  94.1  79.40                                    60       95.1    92.9    91.2  90.0  100.00                                   ______________________________________                                    

The results reported in table V show the advantage of extracting themetals at a temperature of at most 40° C.

EXAMPLE 6

The metals extraction treatment according to mode A of example 1 isrepeated with varying concentrations of stabilized hydrogen peroxideaccording to the invention.

The demetallation rates and hydrogen peroxide consumptions are reportedin table VI

                  TABLE VI                                                        ______________________________________                                        H.sub.2 O.sub.2 /H.sub.2 O    H.sub.2 O.sub.2                                 concentration                                                                           demetallation rate (% by weight)                                                                  consumption                                     (% by weight)                                                                           V       Ni      Fe    Mo    (mole %)                                ______________________________________                                         3        71.0    52.1    70.0  69.0  82.5                                     6        78.0    66.2    72.0  70.0  44.8                                     9        85.3    80.2    75.0  71.0  33.0                                    15        92.7    85.7    82.1  83.1  36.1                                    20        93.1    86.6    83.9  84.9  40.1                                    30        94.4    88.1    85.1  89.5  44.7                                    ______________________________________                                    

The object of the following examples 7 to 9 is to illustrate thestabilizing effect of the hydrogen peroxide aqueous solutions in thepresence of various stabilizing agents according to the invention.

EXAMPLE 7

Example 1 is repeated with varying amounts of consumed stabilizingorganic compound.

The results are reported in Table VII.

                  TABLE VII                                                       ______________________________________                                        L (+) ASCORBIC   DEMETALLATlON RATE                                           ACID CONCENTRATION                                                                             (% by weight)                                                (g/l)            V       Ni      Fe    Mo                                     ______________________________________                                        0.55             67.5    62.6    57.0  52.5                                   2.50             76.2    71.0    66.0  60.9                                   4.50             85.5    80.2    75.0  71.0                                   6.50             86.2    80.9    75.9  70.5                                   12.00            84.3    79.2    74.5  68.6                                   14.80            83.9    78.8    73.2  68.1                                   ______________________________________                                    

EXAMPLE 8

In order to make sure that L(+) ascorbic acid used according to theinvention to stabilize hydrogen peroxide has the same stabilizing effectwith respect to inorganic carriers other than macroporous alumina of a105 cc/100 g porosity and a 110 m² /g specific surface, example 7 hasbeen repeated with carriers of varying nature, the hydrogen peroxidesolution being stabilized at a constant concentration of 4.5 grams/literin all the tests whose results are reported in table VIII.

                  TABLE VIII                                                      ______________________________________                                                                      VANADIUM                                                 SPECIFIC   PORE      DEMETALLATION                                   CARRIER  SURFACE    VOLUME    RATE                                            NATURE   (m.sup.2 /g)                                                                             (cm.sup.3 /100 g)                                                                       (% by weight)                                   ______________________________________                                        ALUMINA   12        39        84.2                                                      90        65.3      83.2                                                     230        60.7      70.4                                                     110        105       85.3                                            SILICA   255        81        80.1                                            SILICA-  380        90        83.1                                            ALUMINA                                                                       ZEOLITE  261        53        75.1                                            ______________________________________                                    

EXAMPLE 9

The metal extraction treatment according to mode A of example 1 isperformed with the use of different stabilizing agents or mixturesthereof, at the same concentration of 4.5 grams/liter in all the tests.

The results are reported in table IX.

                  TABLE IX                                                        ______________________________________                                                  demetallation rate  H.sub.2 O.sub.2                                 stabilizing                                                                             (% by weight)       consumption                                     agent     V        Ni     Fe   Mo     (mole %)                                ______________________________________                                        Citric acid*                                                                            87.3     82.1   77.3 84.4   38.7                                    Maleic acid*                                                                            67.6     63.3   60.  64.2   16.9                                    Oxalic acid*                                                                            79.4     74.5   71.0 70.1   18.2                                    Salycilic acid**                                                                        85.9     81.2   76.8 76.5   17.5                                    Glycolic acid*                                                                          75.1     70.3   68.3 67.0   20.1                                    ______________________________________                                         *Aqueous solution of 9% by weight hydrogen peroxide content                   **Aqueous solution of 20% by weight hydrogen peroxide content            

The stabilization of hydrogen peroxide by organic compounds always giveshigh demetallation rates. However the peroxide consumption balance seemsto indicate that the rate of decomposition of hydrogen peroxide by theextracted metal ions, at the level of the catalyst bed subjected toextraction, depends on the nature of the stabilizing compound. Theresults of these tests show that the best hydrogen peroxide stabilizers,for the regeneration of catalysts contaminated by metals from thevanadium, nickel and iron group, are salicylic acid, citric acid, maleicacid, oxalic acid, L(+) ascorbic acid and glycolic acid.

EXAMPLE 10

The object of this example is to illustrate and compare the catalyticactivities of catalysts initially comprising nickel, molybdenum andalumina, respectively is after use and after regeneration according tothe invention. After regeneration, these catalysts have been reactivatedby roasting and sulfurization in the conditions of example 1.

A deasphalted BOSCAN oil containing 550 ppm of vanadium, 60 ppm ofnickel, 5.06% of sulfur, is hydrotreated in the following operatingconditions: temperature of 380° to 400° C., total pressure of 100 bars,VVH of 1, hydrotreatment time of 100 hours. The nickel and vanadiumhydrodemetallation rates of the charge and the hydrodesulfurizationrates are reported in table X.

                                      TABLE X                                     __________________________________________________________________________           nickel and                                                                    vanadium                                                                              hydro    physical characteristics                                     demetallation                                                                         desulfurization                                                                        of the catalysts                                             rate of the                                                                           rate of the                                                                            pore                                                         charge  charge   volume                                                                             specific                                                (% by weight)                                                                         (% by weight)                                                                          (cm.sup.3 /                                                                        surface                                                                           density                                             380° C.                                                                    400° C.                                                                    380° C.                                                                     400° C.                                                                    100 g)                                                                             (m.sup.2 /g)                                                                      (cm.sup.3 /g)                                __________________________________________________________________________    Fresh  84  96  34   54  105  110 0.75                                         catalyst                                                                      Ni.Mo/                                                                        Al.sub.2 O.sub.3                                                              Used   43  55  27   40  5-6  10-15                                                                             2.50                                         catalyst                                                                      Catalyst                                                                             69  85  30   49  86.2 82.1                                                                              0.96                                         regenerated                                                                   according                                                                     to the                                                                        invention                                                                     (mode A)                                                                      __________________________________________________________________________

Although the metal extraction from the used catalyst is limited,according to the invention, to 85% (mode A of example 1) the so-treatedand reactivated catalyst has a pore volume and a specific surfaceclearly higher than those of the used catalyst.

The catalytic activity for hydrodemetallation of the charge by removingnickel and vanadium contained therein and the hydrodesulfurizingactivity are close to those of the fresh catalyst. The results show thepossibility of recovering, as compared with the fresh starting catalyst,a hydrodemetallation catalytic activity, with respect to nickel andvanadium of the charge of 69:84, i.e. 82% at 380° C .and 85:96, i.e.88.5% at 400° C., and a hydrodesulfurizing activity of 30:34, i.e. 88%at 380°°C and 49:54, i.e. 90.7% at 400°°C.

Hence, the regeneration process of the invention is applicable tohydrodemetallation as well as to hydrodesulfurization of a heavy oilcharge.

EXAMPLE 11

This example illustrates the activities of regenerated catalyst ofexample 1 initially comprising nickel and molybdenum according to theinvention (test of roasting and test of metal extraction example 1, testA) after several recyclings.

After each hydrotreatment in the same operating conditions as in theexample 10, except the time for the test was 1000 hours instead of 100hours, the catalyst was regenerated and reactivated under the conditionsof example 1. The same catalyst was so used four times (fourrecyclings).

The nickel and vanadium hydrodemetallation rates of the charge and thehydrodesulfurization rates are reported in table XI. The results showthat the catalytic activities are substantially the same after fourrecyclings.

                  TABLE XI                                                        ______________________________________                                                 Nickel and vanadium                                                           demetallation rate                                                                         Hydrosulfurization                                               of the charge                                                                              rate of the charge                                               (% by weight)                                                                              (% by weight)                                                    380° C.                                                                       400° C.                                                                          380° C.                                                                         400° C.                             ______________________________________                                        Successive                                                                             1st   68       84      27     47                                     recyclings                                                                             2nd   67.8     84      26     46.5                                   of       3rd   67.1     83.2    25     45.8                                   regenerated                                                                            4th   66.5     82.5    24.5   45                                     catalyst                                                                      ______________________________________                                    

EXAMPLE 12

This example compares the catalytic activities of catalysts initiallycomprising cobalt, molybdenum and alumina, respectively, fresh andregenerated according to the invention.

A Co-Mo catalyst, initially comprising 2.36% by weight of cobalt, 9.33%by weight of molybdenum, 0% by weight of vanadium and 0% by weight ofnickle on a macroporous alumina inorganic carrier having a porosity of60 cm³ /100 g and a specific surface of 200 m² /g was activated in thesame operating conditions as in the example 1.

It was then used in the hydrotreatment of a reduced Safanyia crude oilhaving a density of 0.975 g/cm³ and containing 4.15% by weight ofsulfur, 6.50% by weight of asphaltenes, 12% by weight of Conradsoncarbon, 26 ppm of nickel, 82 ppm of vanadium, in the following operatingconditions:

    ______________________________________                                        VVH = 0.3          T = 385° C.                                                                       P = 140 bars                                    H.sub.2 /hydrocarbons = 1000 l/l                                              Hydrotreatment time = 8000 hours.                                             ______________________________________                                    

After 8000 hours of operation, the used catalyst contained (in % byweight):

    ______________________________________                                        sulfur:       12%      Carbon:    15.5%                                       Vanadium:   10.5%      Nickel:    4.50%                                       ______________________________________                                    

According to the invention as in example 1 (step of roasting and step ofmetal extraction test A, example 1), the catalyst was regenerated andthe demetallation rate of the catalyst was the following:

    ______________________________________                                        Vanadium:   84.7%     Cobalt:      74.9%                                      Nickel:     81.2%     Molybdenum:  69.8%                                      ______________________________________                                    

The catalyst was then reactivated by roasting and sulfurization as inexample 1 for another hydrotreatment of the same Safanyia oil under thesame conditions as above.

The hydrodesulfurization rate and the nickel and vanadiumhydrodemetallation rate of the charge are reported in Table XII.

                  TABLE XII                                                       ______________________________________                                                              Hydrodemetallation                                               Hydrodesulfurization                                                                       rate of the charge                                               rate of the charge                                                                         (% by weight)                                                    (% by weight)                                                                              Ni       V                                              ______________________________________                                        Hydrotreatment                                                                           8000           8000     8000                                       time (hours)                                                                  Fresh catalyst                                                                           72             4.5      10.5                                       Regenerated                                                                              69.5           4.1       9.6                                       catalyst                                                                      ______________________________________                                    

EXAMPLE 13

The same used catalyst as in the example 1 was regenerated according to,test A of example 1 except that ascorbic acid was replaced by nitricacid in the same molar concentration.

After demetallation, the catalyst was separated from the aqueous phase.The analysis of the filtrate by atomic absorption showed that 8.3% ofthe alumina carrier was dissolved.

For comparison, it has been checked with the oxalic acid, the L(+)ascorbic acid, the citric acid, the maleic acid, the salycilic acid andthe glycolic acid that the carrier was not substantially attacked.

What is claimed as the invention is:
 1. A process for regenerating an atleast partially deactivated sulfur-containing catalyst after its use forthe hydrotreatment of a hydrocarbon charge containing sulfur, and atleast one vanadium, nickel or iron metal, said deactivation resultingfrom the deposit of at least one of said metals onto the catalyst, saidcatalyst initially comprising an inorganic carrier and at least oneactive metal or compound of an active metal selected from the groupconsisting of nickel, cobalt and molybdenum, said process consistingessentially of the following successive steps:(a) the sulfur-containingdeactivated catalyst is roasted in the presence of an oxygen-containinggas at 300°-600° C., so as to remove at least 90% of the sulfur, (b) thecatalyst obtained in step (a) is contacted with a hydrogen peroxideaqueous solution containing at least one organic compound comprising astabilizing amount of a carboxylic acid, a carboxylic acid having atleast one alcohol group, or a mixture thereof so as to remove at least10% of the deposited vanadium, nickel or iron metals, and (c) theregenerated catalyst is separated from the hydrogen peroxide aqueoussolution.
 2. A regeneration process according to claim 1, wherein theorganic compound is a mono-carboxylic acid, a mono-carboxylic acidhaving at least one alcohol group, a poly-carboxylic acid having atleast one alcohol group, or a mixture thereof.
 3. A regeneration processaccording to claim 1, wherein the organic compound is selected from thegroup consisting of L(+) ascorbic acid, citric acid, salicylic acid,maleic acid, oxalic acid and glycolic acid.
 4. A regeneration processaccording to claim 1, wherein the inorganic carrier of the catalyst isalumina, silica, a silica-alumina or a zeolite carrier.
 5. Aregeneration process according to claim 1, wherein the catalyst roastingstep is conducted with an oxygen-containing gas providing at least 2moles of oxygen per gram-atom of sulfur and at such a flow rate thatsulfur dioxide formed during roasting is, at any time, lower than 10ppm.
 6. A regeneration process according to claim 1, wherein thehydrogen peroxide concentration in water is from 0.5 to 70% by weight,the concentration of organic compound from 0.1 gram per liter up tosaturation and the extraction temperature of the metals from 0° to 80°C.
 7. A regeneration process according to claim 1, wherein the hydrogenperoxide concentration in water is from 1 to 30% by weight, the organiccompound concentration from 2 to 10 grams per liter and the temperaturefrom 10° to 40° C.
 8. A regeneration process according to claim 1,wherein step (b) is performed in the absence of light, at a flow rate of0.5 to 30 liters per hour of hydrogen peroxide solution per kilogram ofroasted catalyst, for 1 to 6 hours.
 9. A regeneration process accordingto claim 1, wherein the hydrogen peroxide aqueous solution in step (c)is thereafter contacted with a complexing resin having a complexingpower for the metals of the solution, and the recovered hydrogenperoxide solution is free of at least the major part of the metals. 10.A regeneration process according to claim 1, wherein the aqueoussolution of metal ions separated in step (c) is thereafter contactedwith a complexing resin comprising at least one functional group havinga complexing power for ions of metals from the vanadium, nickel and irongroup, at a flow rate of 0.5 to 30 liters per hour per kilogram ofresin, for 1 to 6 hours and at a temperature of 0° to 80° C., andwherein the complexing resin is thereafter subjected to a regenerationstep for recovering the metals therefrom.
 11. A process according toclaim 5, wherein the roasting temperature is about 450°-550° C., theratio of moles of oxygen gas/gram-atom of sulfur is at least 10, and theroasting time is 2-7 hours for catalysts of a sulfur content of about 3%by weight or less and is 8-15 hours for catalysts of a sulfur contenthigher than about 3% by weight.
 12. A process according to claim 1,wherein said catalyst comprises nickel and molybdenum as active metals.13. A process according to claim 1, wherein said catalyst comprisescobalt and molybdenum as active metals.
 14. A process according to claim1, wherein said roasting step is conducted essentially in the absence ofsteam.
 15. A process according to claim 1, wherein said catalyst isarranged as fixed bed, fluid bed, moving bed or expanded bed.
 16. Aprocess according to claim 1, wherein the hydrocarbon charge furthercontains oxygen or nitrogen heteroelements.